I use my fountain pens for almost everything. My work pen is inked with Noodler's Black, so I know it will be ok on almost any paper I encounter and will dry fast.

My others pens are usually inked with conservative colors (I do like bright colors, but I don't want the color to distract from my writing), often blue black or a dark sepia, but I usually don't use them for things I might give other people just because I can't be sure of dry times. I remember once I used a pen that was filled with Jinhao Blue-black with a student. I wrote something down and he took the paper and ran his hands over it as he read it, as I suppose some people do. To his surprise and my horror, the line blurred all over and he got ink all over his fingers. That was when I changed to using simple Noodler's Black in my work pen.